Delta Sigma Modulator and Delta Sigma Analog-Digital Converter

Inactive Publication Date: 2008-10-23
NAGOYA UNIVERSITY
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0024]It is possible, by setting the center oscillation frequencies of the first oscillating means and the second oscillating means higher than a target center oscillation frequency of the frequency modulation signal, to lessen the requirement of linearity required for both oscillating means.
[0025]For the ΔΣ modulator of a feedback system, a higher-order ΔΣ modulator is generally constituted by increasing the number of integrators and feedbacks. By constituting a high-order ΔΣ modulator, it is possible to move quantization noise to a higher frequency area, thereby increasing the S/N ratio. Therefore, there is a demand for constituting a high-order ΔΣ modulator using a ΔΣ modulator of a frequency modulation system.
[0026]Though it is possible to constitute a high-order ΔΣ modulator by employing integrators and feedbacks for a ΔΣ modulator of a frequency modulation system, it is

Problems solved by technology

However, it is difficult to maintain the linearity in the wide frequency modulation range, a

Method used

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  • Delta Sigma Modulator and Delta Sigma Analog-Digital Converter
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second embodiment

[0119]A description will now be given of a ΔΣ modulator according to a second embodiment of the present invention. FIG. 5 is a block diagram showing a configuration of the ΔΣ modulator according to the second embodiment. As FIG. 5 clearly shows, the ΔΣ modulator according to the second embodiment has a configuration approximately similar to that of the ΔΣ modulator according to the first embodiment, and is different only in frequency modulation signals input to the mixer 12.

[0120]The second embodiment includes two voltage-controlled oscillators 10a and 10b. A signal f1 is obtained by frequency modulation by the voltage-controlled oscillator 10a. A signal f2 is obtained by frequency modulation by the voltage-controlled oscillator 10b. The signal f1 and the signal f2 are mixed by the mixer 12. An analog signal input to the voltage-controlled oscillator 10b is complementary in polarity with respect to an analog signal input to the voltage-controlled oscillator 10a. Therefore, if the si...

third embodiment

[0128]A description will now be given of a ΔΣ modulator according to a third embodiment of the present invention. FIG. 6a shows a configuration of the ΔΣ modulator according to the third embodiment. The ΔΣ modulator according to the third embodiment includes an integrator 22 which receives an analog signal, a first-order ΔΣ modulator 34 connected to the integrator 22, a differential circuit (register 36 and adder 38) connected to the first-order ΔΣ modulator 34, an upper limit detector 24 connected to the integrator 22, and a digital signal processing circuit 40 connected to the differential circuit and the upper limit detector 24.

[0129]The integrator 22 integrates an analog signal input from an input terminal. The analog signal input to the integrator 22 is adjusted so as to be a positive value by adding a proper DC bias voltage. As a result, an output of the integrator 22 monotonically increases as time elapses. Since the output of the integrator 22 monotonically increases, the ou...

fourth embodiment

[0144]A description will now be given of a ΔΣ modulator according to a fourth embodiment of the present invention. FIG. 9 shows a configuration of the ΔΣ modulator according to the fourth embodiment. The ΔΣ modulator according to the fourth embodiment is a so-called MASH type ΔΣ modulator. This ΔΣ modulator includes a ΔΣ modulator (42, 44, 46, 48) on a first stage, and a ΔΣ modulator 54 on a second stage.

[0145]The ΔΣ modulator on the first stage is a ΔΣ modulator of feedback system. In other words, the ΔΣ modulator on the first stage includes an integrator 44 which integrates an input signal, a quantizer 46 which quantizes an output of the integrator 44, a digital-analog converter 48 which converts a digital output of the quantizer 46 into an analog signal, and an adder 42 which inverts the polarity of the analog signal converted by the digital-analog converter 114 and adds the inverted analog signal to the input analog signal.

[0146]The ΔΣ modulator on the first stage is connected t...

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Abstract

The present invention provides a ΔΣ modulator of a frequency modulation system that can lessen the requirement of linearity for an oscillator.
A ΔΣ modulator comprises an oscillating apparatus that changes a frequency thereof according to an input signal, a quantizing means for quantizing a frequency modulation signal output from the oscillating apparatus, and an operation means for applying an operation to a digital signal output from the quantizing means. The oscillating apparatus comprises an oscillator that changes a frequency thereof according to the input signal, a reference signal source that outputs a reference signal at a predetermined frequency, a mixer that receives the signals from the oscillator and the reference signal source, and a low-pass filter that passes a low frequency component of a signal output from the mixer. The center oscillation frequency of the oscillator is set higher than a target center oscillation frequency of the frequency modulation signal.

Description

TECHNICAL FIELD[0001]The present application claims priority based on Japanese Patent Application No. 2005-35196 filed on Feb. 10, 2005. The entire contents of the application are incorporated herein by reference.[0002]The present invention relates to a ΔΣ analog-digital converter of the ΔΣ modulation type. More particularly, the present invention relates to improvements of a ΔΣ modulator employed by a ΔΣ analog-digital converter.BACKGROUND ART[0003]A ΔΣ analog-digital converter is known as a converter which can convert an analog signal into a digital signal. FIG. 30 is a block diagram showing a basic configuration of the ΔΣ analog-digital converter. The ΔΣ analog-digital converter includes a ΔΣ modulator 116, and a digital filter 118 connected to the ΔΣ modulator 116.[0004]The ΔΣ modulator 116 samples an input analog signal at a predetermined sampling frequency (a frequency higher than the Nyquist frequency) to convert the analog signal into a pulse density signal. The digital filt...

Claims

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Application Information

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IPC IPC(8): H03M3/02
CPCH03M3/458
Inventor MAEZAWA, KOICHIMIZUTANI, TAKASHI
Owner NAGOYA UNIVERSITY
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